The applicant of the present application has developed a cell (hereinafter, called a quantum cell) utilizing a photoexcited structural change of a metal oxide semiconductor with ultraviolet irradiation (Patent Document 1). The secondary cell disclosed in Patent Document 1 is safe as being an all-solid-state type without causing any chemical reaction during charging-discharging processes and is expected to be a technology being superior to a lithium ion cell in terms of output density and power density. The secondary cell in Patent Document 1 has a structure including a first electrode, an n-type metal oxide semiconductor layer, a charging layer, a p-type semiconductor layer, and a second electrode that are layered on a substrate.
In Patent Document 1, the charging layer is formed with a coating pyrolysis method. Specifically, the charging layer is formed by performing a coating step, a drying step, a burning step, and an ultraviolet irradiating step in the order thereof.